As the volume of information exchanged electronically grows, so does the need to organize it in a way that facilitates storage and future retrieval. Communication clients, particularly email clients, have become a repository of valuable data. Productivity of knowledge workers depends on the ability to find a requested piece of information that very often has arrived as an email or attachment.
The traditional way to organize email data uses a folder hierarchy, similar to the folder hierarchy of conventional file systems. In theory, the folder hierarchy is the ultimate classification—being completely user defined, it has the potential to be the best representation of user intentions. Unfortunately, it does not always work so well in practice.
The main problem with the folder classification system is that it does require an explicit user action, whether it is filing the message in the appropriate folder, or creating a rule to do so automatically. With the current volume of email communication, the job quickly becomes a chore that few users can maintain. Some user surveys have shown that many users simply give up on folder classification, keeping all or most of their incoming messages in the inbox and finding requested items by sorting and searching.
Even for those users who do file all the mail items on a regular basis, the folder system does not often work as well as expected. The problem is the discrepancy between the dynamic nature of interpersonal contacts and the static folder structure. Even the best designed folder hierarchy (and few real users are experts in the taxonomy necessary to create the “best” hierarchy,) becomes partially obsolete after a period and should be redesigned. However, the labor cost of re-classifying all the items, especially those in the archives, is very high and usually not justified by the added benefit of the new organization. Some users complained that in the end, the obsolete folder structure often becomes an obstacle rather then an advantage, as the user does not always remember where the item was placed.
There have been many attempts to organize email communications automatically. Many email clients allow creating automatic rules to move new messages into appropriate folders, but automatic removal of new messages from inbox also removes them from user focus.
Another approach is to use standing queries. For example, a query may look for all mail items involving a given person as a sender or recipient. Standing queries allow grouping messages without taking them out of the inbox. Some authors proposed a predefined set of standing queries that can be used to organize the inbox. However, the drawback of a predefined set is in the limited number of categories: it does not scale well when the number of contacts grow.